1. Field of the Invention
The present invention relates to a method for forming an array substrate and, most particularly, to use of a laser ablation process to manufacture the array substrate.
2. Description of the Related Art
Liquid crystal display (LCD) operation, in which angles of liquid crystal molecules are changed to control light transmission, conventionally requires a liquid crystal layer disposed between a color filter substrate and a thin film transistor (TFT) array substrate. As shown in FIGS. 1A-1E, TFT array substrate fabrication comprises five photo mask processes. A display region (not shown) of the substrate 10 has plurality of pixels, each defined in two areas, with area I acting as a TFT and area II acting as a storage capacitor. FIG. 1A shows a metal layer formed on the substrate 10, patterned by a first photo mask, forming a gate electrode 11A in area I and a bottom electrode 11B in area II, respectively. As shown in FIG. 1B, a dielectric layer 12, a semiconductor layer, and a doped semiconductor layer are sequentially formed on the structure and patterned by a second photo mask, forming a channel layer 13 and an ohmic contact layer 14 in area I. As shown in FIG. 1C, a metal layer is formed and patterned by a third photo mask to form source/drain electrodes 15. The ohmic contact layer not masked by the source/drain electrodes 15 is etched simultaneously. As shown in FIG. 1D, a passivation layer 17 is formed and patterned by a fourth photo mask to form a contact hole 16 exposing a part of the drain electrode 15 of the TFT. A conductive layer is then formed overlying the structure and patterned by a fifth photo mask. As shown in FIG. 1E, the patterned conductive layer 18 acts as a top electrode in area II and pixel electrode (not shown) electrically connecting to the drain electrode 15 through the contact hole 16 (see FIG. 1D).
In addition to the lithography process, organic or inorganic material layers can be patterned by laser ablation such as disclosed in U.S. Pat. Pub. No. 2005/0242365, 2006/0003553, 2005/0247950. The laser ablation cannot selectively pattern, it is necessary to use a photo mask, thereby increasing costs. Compared to other lithography light sources, large area exposure is difficult in laser source. The photo mask alignment also complicates the machine integration. Accordingly, a selective laser ablation process requiring no photo mask is called for.